Data Transfer Apparatus, Storage Device Control Apparatus and Control Method Using Storage Device Control Apparatus

ABSTRACT

A data transfer apparatus includes a memory having first and second queues for storing data transfer information that includes information specifying a first memory area and information specifying a second memory area, a first processor which registers the data transfer information in the first or second queue, and a second processor performing a processing to transfer data stored in the first memory area to the second memory area. The second processor reads out the data transfer information registered in the first queue, transfers the data based on the read data transfer information, and decides if data transfer information succeeding to the read data transfer information is registered in the first queue. If the succeeding data transfer information is registered, the second processor reads out the succeeding data transfer information from the first queue, and performs the data transfer processing based on the read data transfer information.

The present application claims priority from Japanese applicationJP2003-400512 filed on Nov. 28, 2003, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to data transfer apparatus, storage devicecontrol apparatus and control method using the storage device controlapparatus.

Data has so far been transferred directly between memory and device notthrough CPU by the widely used DMA transfer technique using a DMA(Direct Memory Access) controller. When the DMA transfer occurs, the CPUgives the DMA controller the information necessary for the data transfersuch as the transfer source and destination so that the information canbe set in the controller, and commands it to make the data transferprocessing. The DMA controller, when instructed to do the data transferprocessing, transfers data not through the CPU. For example, refer toJP-A-2003-91497.

SUMMARY OF THE INVENTION

In the conventional DMA transfer processing, however, since the CPUdirectly sets the information such as data source and destination in theregister of the DMA controller, it takes a considerable amount of timefor the CPU to set this information in the DMA controller particularlywhen the data transfer processing is made at frequent intervals. Inaddition, when the DMA controller finishes the data transfer processing,it informs the CPU of this fact by a process like interruption. However,as the data transfer processing is frequently made, this notice from theDMA controller to the CPU happens quite often, thus frequentlyinterrupting the CPU's operation.

In view of this background, the invention is to provide a data transfercontrol method, data transfer apparatus, storage device controlapparatus, control method using the storage device control apparatus,and channel adapter that all can make efficient use of the CPU.

According to this invention, there is provided a data transfer apparatusthat includes a memory having first and second queues for storing datatransfer information that includes information for specifying a firstmemory area and information for specifying a second memory area, a firstprocessor for causing the data transfer information to be registered inthe first or second queue, and a second processor for making datatransfer processing to transfer data stored in the first memory area tothe second memory area, wherein the second processor reads out the datatransfer information registered in the first queue, makes the datatransfer processing on the basis of the read data transfer information,and decides if the data transfer information that follows the read datatransfer information is registered in the first queue, in which case, ifthe succeeding data transfer information is registered in the firstqueue, the second processor reads out the succeeding data transferinformation from the first queue, and makes the data transfer processingon the basis of the read data transfer information, while if thesucceeding data transfer information is not registered in the firstqueue, the second processor reads out the data transfer information fromthe second queue, and makes the data transfer processing on the basis ofthe read data transfer information.

The invention provides a data transfer apparatus, a storage devicecontrol apparatus and a control method using the storage device controlapparatus that all can make efficient use of the CPU.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a computer according to the firstembodiment of the invention.

FIG. 2 is a diagram showing one example of data transfer informationaccording to the first embodiment of the invention.

FIG. 3 is a flowchart showing the flow of data transfer processingaccording to the first embodiment of the invention.

FIG. 4 is a flowchart showing the flow of processes for DMA controller60 to stop the data transfer processing according to the firstembodiment of the invention.

FIG. 5 is a block diagram showing the whole arrangement of aninformation processing system as the second embodiment of the invention.

FIG. 6 is a block diagram showing the hardware construction of channelcontrol unit 210 according to the second embodiment of the invention.

FIG. 7 is a block diagram showing the construction of data transfer LSI500 according to the second embodiment of the invention.

FIG. 8 is a table showing the details of data transfer information thatthe data transfer LSI 500 needs for data transfer according to thesecond embodiment of the invention.

FIG. 9 is a table showing one example of end status information that thedata transfer LSI 500 writes in local memory 212 when the data transferLSI 500 finishes data transfer according to the second embodiment of theinvention.

FIG. 10 is a table showing the registers that the data transfer LSI 500has according to the second embodiment of the invention.

FIG. 11 is a flowchart showing the flow of the data transfer processingusing a transfer information list according to the second embodiment ofthe invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention will be described in detail with referenceto the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram of a computer according to the firstembodiment of the invention.

The computer 1 has a CPU 10, a RAM 20, a storage unit 30, an input unit40, an output unit 50, a DMA controller 60 and an I/O interface 70.

The CPU 10 is a processor for controlling the whole computer 1. The CPU10 timely reads out a program from the storage unit 30, writes the readprogram in the RAM 20, and executes the program stored in the RAM 20 torealize various different functions.

The storage unit 30 may be any storage unit such as a hard disk,flexible disk or semiconductor storage unit. The storage unit 30 may beconnected to the outside of computer 1 as illustrated or incorporatedwithin computer 1 to be integral therewith. The input unit 40 is adevice that is used for the user to enter data into computer 1, such asa keyboard or mouse. The output unit 50 is a device that is used forproducing information to the outside, such as a display or printer.

The I/O interface 70 is an interface through which the computer 1communicates with external apparatus. The I/O interface 70 is, forexample, a communications interface that is connected to LAN (Local AreaNetwork) or an RS 232C interface for serial connection. The I/Ointerface 70 has a buffer memory 71 and it is able to store the receiveddata in the buffer memory 71 and transmit the data stored in the buffermemory 71 to the external apparatus under the control of CPU 10.

The DMA controller 60 transfers data between a device and a memory orbetween memories. The DMA controller 60, when starting to transfer datain response to the instruction from CPU 10, is able to continue the datatransfer processing not through the CPU 10. The DMA controller 60 canmake, for example, data transfer processing for transferring databetween the storage unit 30 and the buffer memory 71 of the I/Ointerface 70. The DMA controller 60 has a plurality of registers one ofwhich is a start register 61. The start register 61 is a register forurging the DMA controller 60 to start operating. The DMA controller 60starts to transfer data in response to the writing of a value in thestart register 61.

In addition, another one of the registers that the DMA controller 60 hasis an abort register 62. The abort register 62 is a register forterminating the operation of DMA controller 60. The DMA controller 60ends the data transfer processing when a predetermined value is writtenin the abort register 62. The process for the DMA controller 60 toterminate the data transfer processing will be described later.

The RAM 20 has three queues provided. The term queue is a memory areathat is controlled so that the data stored in the area can be read outaccording to FIFO (First In First Out). A nonpreferential transferinformation queue 21 and a preferential transfer information queue 22are the queues that the CPU 10 uses to register data transferinformation in order to fix necessary data for data transfer such as theaddress of data transfer source and the length of data to betransferred.

The CPU 10 causes data transfer information to be registered in thenonpreferential transfer queue 21 at the time of each different runningtask of processes. The term task is a sequence of processes to beexecuted by CPU 10. The CPU 10 causes data transfer information forhigh-priority data transfer processing to be registered in thepreferential transfer information queue 22. For example, the CPU 10,while executing a high-priority task, is able to make the necessary datatransfer processing be treated as high-priority processing. In addition,it can be considered that the level of the priority to data transferprocessing is previously fixed according to the kind of a task that theCPU 10 performs, and that the RAM 20 or storage unit 30 stores acorresponding table of priority and kind of task (priority manager). Inthis case, the CPU 10 can acquire the priority corresponding to the kindof the running task from the table and determine the queue in which thedata transfer information is to be registered according to the priority.The DMA controller 60 preferentially reads out the data transferinformation registered in the preferential transfer information queue 22over that registered in the nonpreferential transfer information queue21 and performs the data transfer processing associated with thatinformation.

When the DMA controller 60 finishes the data transfer processing, theend status that indicates the result of the data transfer processing isregistered in an end status queue 23. The end status is data that has,for example, an error code or the like fixed. The CPU 10 causes the datatransfer information to be registered in the nonpreferential transferinformation queue 21 or preferential transfer information queue 22. TheDMA controller 60 reads out the data transfer information from thepreferential transfer information queue 22. When the data transferinformation is not registered in the preferential transfer informationqueue 22, the DMA controller 60 reads out it from the nonpreferentialtransfer information queue 21. The DMA controller 60 makes data transferprocessing based on the read data transfer information. The DMAcontroller 60 causes the end status of the data transfer processing tobe registered in the end status queue 23.

(Data Transfer Information)

FIG. 2 shows an example of the data transfer information. The datatransfer information, as illustrated in FIG. 2, has a transfer ID column201, a transfer direction column 202, a disk address column 203, and atransfer length column 204.

The transfer ID column 201 has entries of ID for identifying the datatransfer information. The CPU 10, when generating the data transferinformation, gives it an ID for identifying each piece of data transferinformation, and writes it in the transfer ID column 201.

The transfer direction column 202 has entries of direction values inwhich data is transferred between the storage unit 30 and the buffermemory 71. If “0” is written in the transfer direction column 202, thedata stored in the buffer memory 71 is transferred to the storage unit30. If “1” is written in the transfer direction column 202, the datastored in the storage unit 30 is transferred to the buffer memory 71.

The disk address column 203 has entries of address of storage unit 30.The DMA controller 60 transfers the data stored at the address of diskaddress column 203 in the storage unit 30 to the buffer memory 71 or thedata stored in the buffer memory 71 to the memory area that begins fromthe address of disk address column 203 of the storage unit 30.

The transfer length column 204 has entries of data length that istransferred between the buffer memory 71 and the storage unit 30.

The DMA controller 60 can use the above data transfer information tospecify on the storage unit 30 the memory area that corresponds to thedata length written in the transfer length column 204 and that beginsfrom the address written in the disk address column 203. If “0” iswritten in the transfer direction column 202 of the data transferinformation, the DMA controller 60 makes data transfer so that the dataread from the buffer memory 71 can be transferred to the memory area ofstorage unit 30 that has the data length set as in the transfer lengthcolumn 204 and that begins from the address set in the disk addresscolumn 203.

In this embodiment, it is assumed that the DMA controller 60 alwayswrites at and reads from the same address of the buffer memory 71 andthus that the data transfer information has no description of anyaddress of the buffer memory 71. Of course, it is possible to set anaddress in the buffer memory 71, at or from which the DMA controller 60writes or reads data.

(Data Transfer Processing)

FIG. 3 is a flowchart showing the flow of data transfer processingbetween the buffer memory 71 and the storage unit 30 in this embodiment.

The CPU 10 causes transfer information of data to be registered in thenonpreferential transfer information queue 21 or preferential transferinformation queue 22 of RAM 20 (S3001). The CPU 10 makes a value bewritten in the start register of DMA controller 60 to order it to startthe data transfer processing (S3002).

The DMA controller 60, when detecting that a value has been written inthe start register, decides if data transfer information is registeredin the preferential transfer information queue 22 (S3003). If datatransfer information is registered in the preferential transferinformation queue 22 (S3003: YES), the controller reads out the datatransfer information from the preferential transfer information queue 22(S3004). If data transfer information is not registered in thepreferential transfer information queue 22 (S3003: NO), it reads outdata transfer information from the nonpreferential transfer informationqueue 21 (S3005). The DMA controller 60 makes data transfer processingon the basis of the read data transfer information (S3006). Whenfinishing the data transfer processing, the DMA controller 60 causes theend status be registered in the end status queue 23 (S3007).

On the other hand, the CPU 10, in an interval of the time when it isexecuting other processing, checks if a new end status is registered inthe end status queue 23 (S3008). If the CPU 10 detects that a new endstatus is written in the end status queue 23 (S3008: YES), it makes aprocess corresponding to that end status (S3009). The processcorresponding to the end status is, for example, that when the DMAcontroller 60 abnormally aborted the data transfer processing, a messageor the like indicating that the data transfer processing was failed issent to the output unit 50.

When the succeeding data transfer information is registered in thepreferential transfer information queue 22 or nonpreferential transferinformation queue 21, the DMA controller 60 continues to again processfrom the step (S3003) without waiting for the writing of the startregister.

Although the DMA controller 60 starts to make data transfer processingwhen the CPU 10 writes a value in the start register of DMA controller60 as described above, the DMA controller 60 may observe thepreferential transfer information queue 21 or nonpreferential transferinformation queue 22, and start to make data transfer processing whendetecting that data transfer information is written in the queue 21 or22.

Thus, as described above, the CPU 10 can order the DMA controller 60 tomake a plurality of data transfer processes by successively registeringdata transfer information in the nonpreferential transfer informationqueue 21 or preferential transfer information queue 22. Since the DMAcontroller 60 reads out data transfer information from the preferentialtransfer information queue 22 or nonpreferential transfer informationqueue 21 and makes data transfer processing on the basis of the read-outdata transfer information, it can make data transfer processing in anasynchronous manner independently of the process in which the CPU 10sets necessary data for data transfer processing as the data transferinformation and causes it to be registered in the nonpreferentialtransfer information queue 21 or preferential transfer information queue22.

According to the invention, since the first processor (CPU 10) causesdata transfer information to be registered in the queue (nonpreferentialtransfer information queue 21 or preferential transfer information queue22) provided in the memory (RAM 20), it does not directly interact withthe second processor (DMA controller 60), but it can order the secondprocessor to make the data transfer processing. Therefore, the firstprocessor does not require to receive the end notice from the secondprocessor each time the data transfer processing is finished, and thusit can make other processes. Accordingly, it is possible to efficientlyuse the first processor.

The first processor (CPU 10) is able to control the order of datatransfer processes by, for example, causing the data transferinformation for high-priority data transfer processes to be registeredin the head of the second queue (nonpreferential transfer informationqueue 21). However, if the second processor (DMA controller 60) read thedata transfer information from the second queue during the time in whichthe first processor was changing the order of the pieces of the datatransfer information to be registered in the second queue, the datatransfer processes would not be performed in the order of high-priorityprocesses that the first processor had planned for. Therefore, in orderthat the order of the pieces of the data transfer information registeredin the second queue can be changed to make high-priority processes cometo the beginning, it would be necessary that the first processorinterrupt the operation of the second processor.

However, according to the invention, the second processor preferentiallyreads out the data transfer information registered in the first queue(preferential transfer information queue 22) over that registered in thesecond queue. Therefore, the first processor causes the data transferinformation about high-priority data transfer processes to be registeredin the first queue, thereby achieving the same effect as it registersthe data transfer information in the second queue at the head. Thus, thefirst processor does not need to interrupt the operation of the secondprocessor, while the data transfer processes can be preferentiallyperformed in the order of processes that is specified by the datatransfer information registered in the first queue. In other words, thefirst processor can easily control the order of data transfer processesto be executed.

In addition, the first processor can make the data transfer processes beperformed preferentially according to the data transfer informationregistered in the first queue without changing the order of arrangementof the data transfer information registered in the second queue. Thus,when data transfer information is registered according to the prioritylevel, it is possible to suppress the necessary access to the memory,and hence to achieve efficient data transfer processing.

Moreover, the first processor can grasp the results of the data transferprocessing that the second processor has performed by referring to thememory (end status queue 23). Therefore, the first processor does notneed to receive the notice of having finished processes directly fromthe second processor, but it can acquire the results of the datatransfer processes that the second processor has finished indirectlythrough the memory. Accordingly, the first processor is able toefficiently operate.

In addition, since the clock at which the CPU 10 operates is generallyfaster than that used for the DMA controller 60, the time taken for theCPU 10 to access to RAM 20 is often shorter than that required for it toaccess to the register of DMA controller 60. Therefore, according to theinvention, the CPU 10 requires smaller amounts of time to fix theinformation for the data transfer processes to the DMA controller 60,and thus it can more efficiently operate.

When reading out the data transfer information from the RAM 20, the DMAcontroller 60 may take burst transfer along the bus that connects theDMA controller 60 and the RAM 20. Thus, the DMA controller 60 can readout data along the bus with high utilization efficiency. Thus, the wholecomputer 1 can make efficient transfer processing.

Moreover, in general, when the CPU 10 causes the DMA controller 60 tocontinuously perform data transfer processes, the CPU 10, afterdetecting that the DMA controller has finished data transfer processing,needs to fix necessary information for the successive data transfer inthe DMA controller 60. According to the invention, the CPU 10 can writenecessary information for data transfer processes in the RAM 20irrespective of how the DMA controller 60 is operating. Therefore, theCPU 10 can order the DMA controller 60 to make a plurality of datatransfer processes.

Furthermore, the CPU 10 may fix the degree of priority at each task tobe executed and determine the queue in which data transfer informationis to be registered according to the degree of priority. Thus, the CPU10 can make it possible that the data transfer processes to be executedaccording to a high-priority task can be preferentially performed overthose to be executed according to a low-priority task.

(Data Transfer Aborting Process)

It can be here considered that the data transfer information alreadyregistered in the queue (nonpreferential transfer information queue 21or preferential transfer information queue 22) by the first processor(CPU 10) is, for example, changed in its contents or deleted from thequeue by the first processor. At this time, if the second processor (DMAcontroller 60) read the data transfer information that was being changedby the first processor, and performed the data transfer processing onthe basis of that data transfer information, the data transferprocessing might be made between memory areas different from those onwhich it would be tried to make by the command from the first processor.In addition, if the second processor made data transfer processing onthe basis of the data transfer information that was tried to delete fromthe queue by the first processor, it would end up uselessly making thedata transfer processing. This might reduce not only the efficiency ofthe operation of the second processor but also the data transferefficiency of the whole data transfer apparatus. Therefore, the firstprocessor would need to temporarily stop the second processor from thedata transfer processing and to prevent it from reading out the datatransfer information that the first processor was trying to change ordelete. However, if the data transfer process that was being executed bythe second processor was stopped, it would need to be reattempted, andthus it might take a long time for the data transfer as a whole. Thus,according to the invention, the second processor, after the completionof data transfer processing, detects an abort command in the register(abort register 62), this command indicating to abort the data transferprocessing, and stops the succeeding data transfer processing.

A description will be made of the process for the first processor tostop the second processor from the data transfer processing.

The CPU 10 sets a predetermined value in the abort register 62 of DMAcontroller 60 to order the DMA controller 60 to abort the data transferprocessing. As the predetermined value set in the abort register 62,there are two kinds of commands: an abort command to stop the processingat the time when the data transfer processing based on certain datatransfer information has been finished, and a forced termination commandto immediately stop the running data transfer processing. The abortcommand has a value of, for example, “0x0001”. The forced terminationcommand has a value of, for example, “0x0002”.

FIG. 4 is a flowchart showing the flow of processes for the DMAcontroller 60 to stop the data transfer processing. The CPU 10 causesdata transfer information to be registered in the nonpreferentialtransfer information queue 21 or preferential transfer information queue22 and writes a value in the start register 61 of DMA controller 60,thus causing the DMA controller 60 to start data transfer processing.

The DMA controller 60 reads out the data transfer information from thepreferential transfer information queue 22 when it detects the writingof a value in the start register 61. If no data transfer information isregistered in the queue 22, the controller 60 reads out the datatransfer information from the nonpreferential transfer information queue21 (S4001). The DMA controller 60 starts to transfer data between thebuffer memory 71 and the storage unit 30 on the basis of the read datatransfer information (S4002).

When detecting the writing of a value in the abort register 62 (S4003),the DMA controller 60 refers to the abort register 62 and decides if theforced termination command is set in the abort register 62 (S4004). Ifthis command is set in the abort register 62 (S4004: YES), the DMAcontroller 60 stops the running data transfer processing (S4005). TheDMA controller 60 generates the end status indicating that the datatransfer processing has been forcibly stopped, causes the generated endstatus to be registered in the end status queue 23 (S4006), and ends theoperation.

If the forced termination command is not set in the abort register 62(S4004: NO), the DMA controller 60 continues the data transferprocessing even if the abort command is written in the abort register 62(S4007). The DMA controller 60, after making the data transferprocessing between the buffer memory 71 and the storage unit 30, refersto the abort register, checking if the abort command is set in the abortregister 62 (S4008). If the abort command is set in the abort register62 (S4008: YES), the DMA controller 60 stops the following data transferprocessing. The DMA controller 60 generates the end status indicatingthat the following processing has been stopped, and causes this endstatus to be registered in the end status queue 23 (S4009). If the abortcommand is not set in the abort register 62 (S4008: NO), the DMAcontroller 60 generates the end status indicating that the data transferprocessing has been normally finished, and causes the end status to beregistered in the end status queue 23 (S4010). Then, it proceeds back tostep (S4002), and makes data transfer processing about the succeedingdata transfer information registered in the preferential transferinformation queue 22 or nonpreferential transfer information queue 21.

According to the invention, as described above, the second processor(DMA controller 60) stops the succeeding data transfer processing if theabort command is set in the register (abort register 62) after thecompletion of the data transfer processing. Therefore, the secondprocessor never interrupts the running data transfer processing on theway. In addition, the first processor (CPU 10) is able to send the abortcommand to the second processor, ordering it to abort the processingwithout monitoring if the second processor has completed the datatransfer processing and without receiving the notice of completion fromthe second command. Therefore, the first processor can easily controlthe second processor by setting the abort command in the register of thesecond processor so that when the second processor has completed thedata transfer processing, the succeeding data transfer processing can bestopped. Accordingly, the first processor can make efficient operation,and when the second processor is stopped from the data transferprocessing, the transfer ability of the whole data transfer apparatus(computer 1) can be suppressed up to the minimum from being reduced.

If the first processor cannot confirm that the second processor hasstopped the data transfer processing a certain time after the abortcommand is set in the register of the second processor, it may write theforced termination command in the register so that the second processorcan forcibly terminate the data transfer processing. Thus, if the secondprocessor is brought to the stand-by mode without completing the datatransfer processing, the first processor can control the secondprocessor to forcibly stop the data transfer processing. Therefore, whenthe first processor causes the second processor to stop the datatransfer processing, the second processor can stop the data transferprocessing within a predetermined time after the abort command hasissued. Thus, the first and second processors can contribute toefficient data transfer processing. In addition, it is possible tosuppress the reduction of the data transfer ability of the whole datatransfer apparatus.

Thus, when the DMA controller 60 has finished the data transferprocessing, the CPU 10 can stop the following data transfer processing.When the DMA controller 60 stops the data transfer processing, the CPU10 performs, for example, updates the contents of the data transferinformation registered in the queue (nonpreferential transferinformation queue 21 or preferential transfer information queue 22) ordeletes it from the queue. Then, the CPU 10 writes “0” in the abortregister 62 of DMA controller 60 to clear the abort command or forcedtermination command set in the abort register 62. When a value iswritten in the abort register 62, the DMA controller 60 refers to thevalue set in the abort register 62. If the value set in the abortregister is not the abort command or forced termination command, the DMAcontroller 60 reads out the data transfer information from thepreferential transfer information queue 22 or nonpreferential transferinformation queue 21, and resumes the data transfer processing.

The DMA controller 60 may have, for example, a resume register forresuming the data transfer processing so that the CPU 10 can set a valuein this resume register in place of writing “0” in the abort register62, thus ordering the DMA controller 60 to resume the data transferprocessing.

In addition, the start register, the abort register and the above resumeregister can make, for example, one register (control register). In thiscase, the DMA controller 60 can start, stop, forcibly terminate orresume the data transfer processing depending upon whether “1” is set ornot at a predetermined bit position of the value written in this controlregister.

(Deletion of Registered Data Transfer Information)

When the data transfer information registered in the queue(nonpreferential transfer information queue 21 or preferential transferinformation queue 22) is deleted, the CPU 10 can write a valueinstructing not to make data transfer processing in the transfer lengthcolumn 204 of the data transfer information to be deleted. The valueinstructing not to make data transfer processing is, for example, “0”.It may be a value such as “−1” that is not usually used for data length.When this value instructing not to make data transfer processing is setin the transfer length column 204 of the data transfer information readfrom the preferential transfer information queue 22 or nonpreferentialtransfer information queue 21, it can cause the DMA controller 60 not tomake the data transfer processing.

The CPU 10 is also able to cancel the transfer of data about the datatransfer information already registered in the queue by deleting thedata transfer information from the queue (nonpreferential transferinformation queue 21 or preferential transfer information queue 22).However, also the CPU 10 is able to cancel the transfer of data aboutthe data transfer information registered in the queue only by settingthe value instructing not to make data transfer processing in thetransfer length column 204 of the data transfer information registeredin the queue. In other words, the CPU 10 can achieve the same effect aswhen the data transfer information is deleted from the queue only byupdating the contents of the transfer length column 204 of the datatransfer information registered in the queue. Therefore, the frequencyof the access from the CPU 10 to the RAM 20 is reduced when the CPU 10sets a value in the transfer length column of the data transferinformation registered in the queue rather than when it deletes the datatransfer information from the queue. Thus, the access from the CPU 10 tothe RAM 20 becomes less severe as a burden on the data transferprocessing, so that the CPU 10 can efficiently operate. In addition,when deleting the data transfer information from the queue, the CPU 10causes the DMA controller 60 to stop the data transfer processing.Therefore, the frequency of the access from the CPU 10 to the RAM 20 isreduced, thus shortening the processing time necessary to cancel thedata transfer processing so that the time in which the DMA controller 60keeps the data transfer processing interrupted can also be reduced. Thiscan suppress the reduction of the data transfer ability of computer 1due to the canceling of the data transfer processing.

Thus, by alleviating the load of processing on the CPU 10 and shorteningthe time in which the DMA controller 60 is kept stopped from processing,it is possible to improve the efficiency of data transfer processing ofthe whole computer 1.

Second Embodiment

A description will be made of another embodiment of the inventionapplied to a storage device control apparatus.

FIG. 5 is a block diagram of the whole construction of an informationprocessing system that will be described as the second embodiment of theinvention.

Information processing apparatus 100 and a storage device controlapparatus 200 are connected to a network 400 so that they can beintercommunicated through the network 400. The network 400 is, forexample, SAN (Storage Area Network). The network 400 may be LAN (LocalArea Network) other than SAN. The protocol for the network 400 may beany one of fiber channel, ESCON (registered trademark), FICON(registered trademark) and SCSI (Small Computer System Interface).

The information processing apparatus 100 is a computer that offersinformation-processing service by using the memory resource that thestorage device control apparatus 200 provides. The informationprocessing service offered by the information processing apparatus 100is, for example, the automatic teller machine system of bank or the seatreservation system of aircrafts. The information processing apparatus100 has a CPU (Central Processing Unit) and a memory so that variousdifferent functions can be created when the CPU executes variousprograms. The information processing apparatus 100 can serve as amainframe computer, workstation, personal computer or the like.

A storage device 300 has multiple disk drives, and supplies memory areasto the information processing apparatus 100. The disk drive may be anyone of, for example, a hard disk drive, flexible disk drive andsemiconductor storage device. The storage device 300 can also be formedas a disk array by using a plurality of disk drives. In this case, thememory areas supplied to the information processing apparatus 100 can beprovided by a plurality of disk drives that are managed by RAID(Redundant Array of Independent Disks).

The storage device control apparatus 200 accepts a request forinput/output of data to the storage device 300 from the informationprocessing apparatus 100, and makes processing about input/output ofdata to the storage device 300. The storage device control apparatus 200includes a channel control unit 210, a shared memory 220, a cache memory230, and a disk control unit 240. The channel control unit 210 hascommunications interfaces through which it communicates with theinformation processing apparatus 100, and a function to receive therequest for input/output of data to the storage device 300 from theinformation processing apparatus 100. The channel control unit 210 isresponsive to the received data input/output request to send a commandto the disk control unit 240, ordering it to make input/output of datato the storage device 300. The disk control unit 240 responds to thiscommand to make processing about the input/output of data to the storagedevice 300. The shared memory 220 is a memory shared by the channelcontrol unit 210 and disk control unit 240, and stores, for example, theabove-given command to control the input/output of data. The cachememory 230 stores data that is transmitted and received between thechannel control unit 210 and the disk control unit 240.

The physical volume as physical memory areas provided by the disk drivesof the storage device 300 has a logic volume set as logic memory areas.The storage device control apparatus 200 controls the input/output ofdata to this logic volume. When the information processing apparatus 100transmits an input/output data request for writing data to the logicvolume (hereinafter, called the data write request) to the storagedevice control apparatus 200, the channel control unit 210 receives thedata write request. The channel control unit 210 responds to thereceived data write request to generate a command to write data(hereinafter, called the data write command) and cause the shared memory220 to store this command. In addition, the data to be written receivedfrom the information processing apparatus 100 is stored in the cachememory 230. The disk control unit 240 reads out the data write commandfrom the shared memory 120 and makes processing by which the data storedin the cache memory 230 is written in the storage device 300 on thebasis of the read command. The data write command stored in the sharedmemory 220 under the control of the channel control unit 210 and thedata written in the cache memory 230 under the control of the channelcontrol unit 210 can also be transmitted directly to the disk controlunit 240 from the channel control unit 210.

(Channel Control Unit)

The channel control unit 210 sometimes makes the following processingexcept the data input/output processing according to the datainput/output request received from the information processing apparatus100.

In some cases, the channel control unit 210 makes, for example, copyingof the data stored in a first logic volume into a second logic volumedifferent from the first logic volume (hereinafter, referred to as localcopy processing) in order to further enhance the maintainability of thedata stored in the first logic volume of the storage device 300.

In addition, the channel control unit 210 sometimes makes copying of thedata stored in the first logic volume into a third logic volume thatother storage device control apparatus 200 controls (hereinafter, calledjournal copy processing) in order to further enhance the maintainabilityof the data stored in the first logic volume. In this case, the channelcontrol unit 210 of the first storage device control apparatus 200 andthe channel control unit 210 of the second storage device controlapparatus 200 are connected so that they can intercommunicate. The firststorage device control apparatus 200 transmits the data stored in thefirst logic volume to the second storage device control apparatus 200.Thus, even if a failure occurs in the first storage device controlapparatus 200, the information processing apparatus 100 is able toaccess to the second logic volume of the second storage device controlapparatus 200, or the so-called fail over can be achieved.

In the case when the channel control unit 210 of the first storagedevice control apparatus 200 transmits the data stored in the firstlogic volume to the second storage device control apparatus 200, thetransmitting of all data stored in the first logic volume each time datais written in the first logic volume will take much time for thetransfer processing and increase the traffic in the communicationpathway. Thus, the channel control unit 210 transmits only theinformation by which the data stored in the first logic volume isupdated (update history). This update history is called journal.

The channel control unit 210, when receiving the data write request forwriting data to the first logic volume from the information processingunit 100, generates the data write command to the first logic volume andcontrols the shared memory 120 to store it (the command may betransmitted to the disk control unit 240). In addition, the channelcontrol unit 210 controls the copy of the data written in the firstlogic volume (hereinafter, called journal data) to be written in thesecond logic volume. Also, the channel control unit 210 generates metadata that includes the time at which the data write command is generated(the time at which the data is written in the first logic volume), theaddress of the first logic volume specified by the data write request,the data length of the written data, and the address of the second logicvolume in which the journal data has been written. The above journal isthe data including this meta data and the journal data. As describedabove, the channel control unit 210 of the first storage device controlapparatus 200 generates the journal in response to the data writerequest (hereinafter, called journal generation processing), andtransmits the generated journal to the second storage device controlapparatus 200. The channel control unit 210 of the second storage devicecontrol apparatus 200 updates the second logic volume on the basis ofthe received journal. The processing for the channel control unit 210 toreceive the journal is called journal acquisition processing. Also, theprocessing that the channel control unit 210 makes to update the logicvolume on the basis of the journal is called restore processing. Thus,the first and second logic volumes can have the same information contentby intercommunication between the two different storage device controlapparatus 200.

Moreover, the channel control unit 210 sometimes makes the processingfor acquiring the data stored in the logic volume in the past (namely,snapshot processing).

The channel control unit 210 receives a command to make the snapshotprocessing (called snapshot command) from the information processingapparatus 100 and starts the snapshot processing according to thereceived snapshot command. When the channel control unit 210 receivesthe data write command to the first logic volume from the informationprocessing apparatus 100 after the start of the snapshot processing, itdoes not cause the data not to be stored in the first logic volume, butgenerates the data write command to write the data in the second logicvolume. The channel control unit 210 makes the address of the firstlogic volume specified by the data write request be associated with thatof the second logic volume in which the data is actually written, andcauses them to be stored as a management table. The channel control unit210 refers to the management table, thereby making it possible to decideif the most recent data to be stored in the first logic volume is storedeither in the first logic volume or in the second logic volume.

The channel control unit 210, when receiving the data read request fromthe information processing apparatus 100, decides if the latest data tobe stored in the address of the first logic volume specified by thereceived data read request is stored either in the first logic volume orin the second logic volume. The channel control unit 210 reads out thecurrent data from the first or second logic volume according to theresult of the decision. The channel control unit 210 sends the read databack to the information processing apparatus 100 in response to the dataread request.

The information processing apparatus 100 can also transmit the snapshotdata read request for reading out the data corresponding to the timepoint at which the snapshot command has been transmitted. The channelcontrol unit 210 can acquire the data corresponding to the time point atwhich the snapshot processing has been started by reading out the datastored in the first logic volume. Therefore, the channel control unit210, when receiving the snapshot data read request, reads out the datafrom the first logic volume and sends it back to the informationprocessing apparatus 100.

When receiving the data write request to the first logic volume, thechannel control unit 210 may copy the data stored in the first logicvolume into the second logic volume, and write the latest data in thefirst logic volume. In this case, when the channel control unit 210receives the snapshot data read request, it reads out the data from thefirst or second logic volume in accordance with the address specified bythe request, and sends it back to the information processing apparatus100.

The storage device control apparatus 200 makes the above local copyprocessing, journal generation processing, journal acquisitionprocessing and restore processing so that the data stored in the logicvolume can be made to have redundancy and to enhance the maintainabilityof the data. In addition, the storage device control apparatus 200 makesthe snapshot processing to thereby read out the data stored in the past.

The construction of the channel control unit 210 will be describedbelow. FIG. 6 is a block diagram of the hard ware construction of thechannel control unit 210. As illustrated in FIG. 6, the channel controlunit 210 has microprocessors 211, local memories 212, communicationsinterfaces 213, buffer memories 214, and a data transfer LSI 500. Theseelements are built within the same unit. The channel control unit 210can be integrally incorporated in the storage device control apparatus200 or constructed as a detachable channel control unit independently ofthe storage device control apparatus 200.

While the channel control unit 210 has four microprocessors 211, fourlocal memories 212, four communications interfaces 213, two buffermemories and one data transfer LSI 500 as shown in FIG. 6, the numbersof those elements are not limited to such numbers. For example, it mayhave a structure having one microprocessor 211 and two data transferLSIs 500. When the channel control unit 210 has a plurality of datatransfer LSIs 500, the microprocessor 211 needs to inform each ofmultiple data transfer LSIs 500 of data transfer information. Accordingto the invention, since the microprocessor 211 can perform theprocessing to be performed next without waiting for the notice from thedata transfer LSI 500, the microprocessor 211 can send the data transferinformation indirectly through a memory to each data transfer LSI 500.Therefore, the efficiency of the data transfer processing can beincreased. The data transfer processing according to this embodimentwill be described later in detail.

The microprocessor 211 is a processor that controls the whole channelcontrol unit 210. The microprocessor 211 performs the above-given localcopy processing, journal generation processing, journal acquisitionprocessing, restore processing and snapshot processing by executing theprogram stored in the local memory 212, thus offering various differentfunctions. The four microprocessors 211 shown in FIG. 6 eachindependently interpret the data input/output request received from thecommunications interfaces 213, and order the data transfer LSI 500 totransfer data according to the received data input/output request andthe disk control unit 240 to read out the data from the storage device300.

Various programs and data are stored in the local memories 212. In thechannel control unit 210 of this embodiment, the microprocessors 211each manage one different local memory 212. The local memories 212 areconnected through buses to the microprocessors 211. In addition, thelocal memories 212 are also indirectly connected through the busesprovided within each microprocessor 211 to the data transfer LSI 500.The local memories 212 store the programs that the microprocessors 211execute and the data utilized by the programs.

The communications interface 213 is an interface that communicates withthe information processing apparatus 100. This interface has acommunications connector for the communication between the interface andthe information processing apparatus 100. In the channel control unit210, the communications interface uses a protocol of, for example, fiberchannel, SCSI, FICON (registered trademark), ESCON (registeredtrademark), ACONARC (registered trademark) or FIBARC (registeredtrademark) to receive the data input/output request transmitted from theinformation processing apparatus 100 according to the protocol. Thecommunications interfaces 213 force the buffer memories 214 to store thereceived data. In addition, the communications interfaces 213 can makethe data stored in the buffer memories 214 be transmitted to theinformation processing apparatus 100.

The microprocessor 211 responds to the data input/output request thatthe communications interface 213 receives from the informationprocessing apparatus 100 to make processing of data input/output to thestorage device 300, for example, to generate the data write command, ashereinafter called the I/O processing. In addition, the microprocessor211 makes other processes such as the above local copy processing,journal generation processing, journal acquisition processing, restoreprocessing and snapshot processing, as hereinafter called the internalprocessing.

The data transfer LSI 500 transfers data between device and memory orbetween memories, as does the DMA controller 60 that the computer 1 hasin the first embodiment mentioned above. In this embodiment, the datatransfer LSI 500 transfers data mainly between the buffer memory 214 andthe cache memory 230. This data transfer processing is performed as apart of the data input/output processing according to the datainput/output request that the storage device control apparatus 200 hasaccepted from the information processing apparatus 100. When thecommunications interface 213 receives the data input/output request, themicroprocessor 211 generates the data transfer information according tothe received data input/output request, and controls the local memory212 to write this generated data transfer information. The data transferLSI 500 reads out the written data transfer information from the localmemory 212, and transfers the data on the basis of the read datatransfer information. If the channel control unit 210 receives the datawrite request from the information processing apparatus 100, the datatransfer LSI 500 transfers to the cache memory 230 the data that isreceived by the communications interface 213 and stored in the buffermemory 214. The data transfer LSI 500 also makes the data transferprocessing between the buffer memory 214 and the cache memory 230 aboutthe data that this storage device control apparatus 200 transmits to orreceives from other apparatus than the information processing apparatus100 as, for example, when it is connected to other different storagedevice control apparatus 200 and copies the data stored in the storagedevice 300 into the corresponding storage device.

(Data Transfer LSI)

FIG. 7 is a block diagram showing the construction of the data transferLSI 500.

The data transfer LSI 500 has DMAs 501, PCI interfaces 502, PCIinterfaces 503, buffer interfaces 504, cache interfaces 505 and a datatransfer information fetch unit 506.

The PCI interfaces 502 are connected to a PCI bus and transmit andreceive data to and from the PCI bus. The data transfer LSI 500 isconnected through the PCI interfaces 502 to the communicationsinterfaces 213.

The PCI interfaces 503 are also connected to the PCI bus, as are the PCIinterfaces 502. The data transfer LSI 500 is connected through the PCIinterfaces 503 to the microprocessors 211 and local memories 212.

The data transfer LSI 500 may be connected through the same PCI bus tothe communications interfaces 213, microprocessors 211 and localmemories 212. In this case, provision of at least one PCI interface willbe sufficient for the data transfer LSI 500. In addition, the PCIinterfaces 502 and PCI interfaces 503 may be connected to externalapparatus through a bus other than the PCI bus.

The buffer memories 214 are used to temporarily store the data that thechannel control unit 210 transmits to or receives from the informationprocessing apparatus 100. The buffer interfaces 504 control thetransmission and reception of data to and from the buffer memories 214.

The cache interfaces 505 transmit and receive data to and from the cachememory 230. The cache interface 505 may have a buffer memory for moreefficient data transfer.

The DMA 501 is, for example, a DMA (Direct Memory Access) processor. TheDMA 501 can transfer the data stored in the memory area of a datatransfer source to the memory area of a data transfer destination byfixing the information for specifying the memory area of the datatransfer source and the memory area of the data transfer destination.The DMA 501 may be other than the DMA processor, for example, a programto be executed on a processor such as the microprocessor or may be alogic circuit incorporated on an IC for special applications.

The data transfer information fetch unit 506 reads out necessaryinformation for data transfer from the local memories 212 and sets it inthe registers of DMAs 501. The data transfer information fetch unit 506can be constructed as, for example, a special-purpose IC ormicroprocessor.

The data transfer LSI 500 may have no data transfer information fetchunit 506, but instead take the construction capable of direct access bythe DMAs 501 to the local memories 212.

(Data Transfer Information)

FIG. 8 is a table showing details of the data transfer informationnecessary for the data transfer LSI 500 to make the data transferprocessing. The data transfer information 600 has a mask column 601, atransfer byte number column 602, a cache address column 603, a CRCcolumn 604, a transfer direction column 605, a flag column 606, anidentification information column 607, a chain flag column 608, an RCRCcolumn 609, a buffer address column 610 and an LRC column 611.

The microprocessor 211 writes a plurality of pieces of data transferinformation 600 continuously in a memory area beginning from apredetermined address of the local memory 212. Thus, the data transferLSI 500 can read out each of a plurality of pieces of data transferinformation continuously from the memory. In other words, a queue inwhich a transfer information list is registered is formed on the localmemory 212.

In addition, the microprocessor 211 manages the data transferinformation 600 necessary for a sequence of data transfer processes sothat a group of data transfer information 600 (hereinafter, called thetransfer information list) formed by a predetermined number of pieces ofdata transfer information 600 can be processed as a unit. The sequenceof data transfer processes means a plurality of data transfer processesthat the data transfer LSI 500 makes, for example, when the memory areaof the data transfer source or transfer destination on the cache memory230 is discontinuous in association with the data transfer to be made inresponse to one data input/output request received by the channelcontrol unit 210.

Each column of data transfer information 600 will be described below.

The mask column 601 has entries of the information indicating whichcolumn values are to be copied into each column of information 600 inorder to inherit the values set in the respective columns of the datatransfer information 600 that the data transfer LSI 500 has processedjust before the data transfer information 600 belonging to the relatedtransfer information list.

The transfer byte number column 602 has entries of values of data lengthto be transferred.

The cache address column 603 has entries of the addresses on cachememory 230 that are used as the source or destination of the datatransfer that the data transfer LSI 500 makes.

The CRC column 604 has entries of error detecting code on the data to betransferred. For example, the microprocessor 211 computes a CRC code byusing the CRC (Cyclic Redundancy Check) on the data to be transferredand sets it on the CRC column 604. The data transfer LSI 500, whenmaking the data transfer, can use the value set in this column to decideif the data to be transferred has error. If the data to be transferredis decided to have error, the data transfer LSI 500 can stop the datatransfer processing.

The transfer direction column 605 has entries of values indicatingwhether the data transfer LSI 500 transfers the data stored in the cachememory 230 to the buffer memory 214 or transfers the data stored in thebuffer memory 214 to the cache memory 230. The transfer direction column605 has, for example, “0” set when the data transfer LSI 500 transfersthe data from the cache memory 230 to the buffer memory 214, or “1” setwhen it transfers the data from the buffer memory 214 to the cachememory 230.

The flag column 606 has entries of information set for various items.The microprocessor 211 can set in the flag column 606 the values, forexample, indicating whether the data error detection is made by usingthe values of the CRC column or whether the writing of data to the diskcontrol unit 240 is made synchronously or asynchronously.

The identification information column 607 has entries of identificationinformation (processing identification information) that themicroprocessor 211 provides for each transfer information list. Thus,the data transfer LSI 500 can continuously read out a sequence of datatransfer information belonging to the same transfer information listfrom the local memory 212.

The chain flag column 608 has entries of flag values indicating whetherthe data transfer information 600 that continues just after a sequenceof data transfer information 600 belonging to the transfer informationlist should be processed or not. The data transfer LSI 500 can decidewhether or not the data transfer information read out from the memorybelongs to the related data transfer information group to be processedby using the values set in the identification information column 607 orchain flag column 608. In addition, the data transfer LSI 500 can readout other data transfer information 600 than that belonging to the datatransfer group of this data transfer information 600, and make datatransfer processing according to that data transfer information.

The RCRC column 609 has entries of error detecting code for the data tobe transferred. The error detecting code set in the RCRC column 609 iscomputed by, for example, CRC. The RCRC column 609 provides the errordetecting code for the data to be transferred when, for example, thisstorage device control apparatus 200 does not transfer data between theinformation processing apparatus 100 and the storage device 300 buttransfers data for the copy (remote copy) to other storage device.Although the RCRC column 609 has entries of the error detecting code setfor the data to be transferred, as does the above CRC column 604, theerror detecting code set in the RCRC column 609 is copied into the endstatus information that will be described later, and written in thelocal memory 212. Thus, the microprocessor 211 can acquire the errordetecting code for the data after the completion of the data transfer.The microprocessor 211 can use, for example, the error detecting codefor the data transferred in the past data transfer processing, which isacquired from the end status information, as the initial values for thecomputation of the error detecting code for the data to be transferred.The microprocessor 211 can compute the error detecting code for thewhole data to be transferred over a plurality of pieces of data transferinformation 600.

The buffer address column 610 has entries of addresses on the buffermemory 214 that are used as the transfer sources or transferdestinations when the data transfer LSI 500 transfers data.

The LRC column 611 has entries of error detecting code for the datatransfer information 600. This error detecting code is, for example, anLRC code computed by LRC. The microprocessor 211 computes the LRC codeby using the values of the mask column 601, transfer byte number column602, cache address column 603, CRC column 604, transfer direction column605, flag column 606, identification information column 607, chain flagcolumn 608, RCRC column 609 and buffer address column 610 together withthe basic address as the initial value at which the data transferinformation 600 is written on the local memory 212.

The data transfer LSI 500 can check to see if the read data transferinformation is correct information by using the error detecting codeincidental to the data transfer information. Thus, the data transferprocessing can be made with higher reliability.

In addition, the microprocessor 211 generates not only the errordetecting code for the data transfer information but also the referenceposition to be computed together for determining the position at whichthe data transfer LSI 500 starts to read out the data transferinformation from the local memory 212. Therefore, the data transfer LSI500 can detect error even if the data transfer information containserror or even if the data transfer LSI 500 reads out the data transferinformation from an erroneous position of the memory.

In this embodiment, the error detecting codes set in the CRC column 604,RCRC column 609 and LRC column 611 of the data transfer information 600are not limited to CRC code and LRC code, but other different codes suchas check sum and hamming code can be used. Moreover, the error detectingcodes set in the CRC column 604, RCRC column 609 and LRC column 611 ofthe data transfer information 600 may be computed by the data transferLSI 500.

Also in this embodiment, although the identification information set inthe identification information column 607 is provided for each transferinformation list, it may be provided for each piece of data transferinformation 600 as a unit. The data transfer LSI 500 makes data transferprocessing on the basis of data transfer information 600, and causes thelocal memory 212 to store the resulting end status information that willbe described later, in association with the identification informationprovided for each transfer information list. Thus, the microprocessor211 can acquire the result of the data transfer processing in units thatare each provided with the identification information.

(End Status Information)

FIG. 9 is a table showing one example of the end status information thatthe data transfer LSI 500 writes in the local memory 212 when the datatransfer LSI 500 finishes the data transfer processing. In thisembodiment, the data transfer LSI 500 generates the end statusinformation for each transfer information list and writes it in thelocal memory 212.

The end status information 700 includes an identification informationcolumn 701, an end status code column 702, a transfer process number 703and an RCRC column 704.

The identification information column 701 has entries of the sameidentification information as that set in the identification informationcolumn 607 of data transfer information 600 read out by the datatransfer LSI 500. Thus, the data transfer LSI 500 makes the end statusinformation 700 correspond to the transfer information list.

The end status code column 702 has entries of values indicating how thedata transfer LSI 500 has finished the data transfer processing. In thisembodiment, when the first bit of each value of the end status codecolumn 702 is “1”, it indicates that the data transfer LSI 500 hasnormally finished the data transfer processing for the correspondingtransfer information list. If the second bit is “1”, it indicates thatthe data transfer LSI 500 has forcibly ended the data transferprocessing according to the forced termination command from themicroprocessor 211. If the third bit is “1”, it indicates that the datatransfer LSI 500 has aborted the data transfer processing according tothe abort command from the microprocessor 211. If the fourth bit is “1”,it indicates that the data transfer LSI 500 has stopped the datatransfer processing due to the error in hardware.

According to the invention, the data transfer information 600 and theend status information 700 are made corresponding to each other by theidentification information that the microprocessor 211 provides to thedata transfer information 600. Therefore, even if multiple pieces of endstatus information 700 coexist in the local memory 212, themicroprocessor 211 can specify which end status corresponds to that forwhich data transfer information 600. In addition, the microprocessor 211can decide if the data transfer LSI 500 has properly processed the datatransfer information 600 and sent the end status information 700 back tothe local memory 212. If the data transfer LSI 500 writes the end statusinformation 700 in the local memory 212 at a known address, themicroprocessor 211 can confirm that the end status information 700written in the local memory 212 by the data transfer LSI 500 correspondsto the data transfer information 600 specified by the microprocessor211. Therefore, the microprocessor 211 examines if the data transfer LSI500 has read out the data transfer information 600 expected by themicroprocessor 211 and if the data transfer LSI 500 has written the endstatus information 700 at the known address on the local memory 212.

The transfer process number column 703 has entries of the number ofpieces of data transfer information 600 that the data transfer LSI 500has processed of the data transfer information 600 belonging to thetransfer information list. The microprocessor 211 specifies, by usingthe chain flag column 608 of data transfer information 600, the numberof pieces of data transfer information 600 to be processed of thetransfer information list by the data transfer LSI 500, and the datatransfer LSI 500 sets the number of actually performed transferprocesses in the transfer process number column 703 of end statusinformation 700. The microprocessor 211 can compare the specified numberof data transfer processes with the number of the processes performed bythe data transfer LSI 500 to decide if the data transfer LSI 500 hascorrectly operated.

The RCRC column 704 has entries of the same values as set in the RCRCcolumn 509 of data transfer information 600. The data transfer LSI 500can also compute the error detecting code for the data to be transferredon the basis of the value set in the RCRC column 509 of data transferinformation 600, and set the result in the RCRC column 704.

According to the invention, since the data transfer information isindirectly sent from the microprocessor 211 to the data transfer LSI 500through the memory, and since the data transfer LSI 500 thus writes theend status information 700 in the memory, the microprocessor 211 canexamine if the data transfer LSI 500 has transferred data by checkingthe written end status after the transfer processing.

The data transfer LSI 500 writes the identification information of thedata transfer information 600 read out from the local memory 212 in theidentification information column 701 of the end status information 700for the data transfer processing. Therefore, even if multiple pieces ofend status information 700 coexist in the local memory 212, themicroprocessor 211 can specify which end status information 700corresponds to which data transfer information 600.

The data transfer LSI 500, when completing the data transfer processing,writes the result as end status information 700 sequentially in a memoryarea of the local memory 212 that begins from a predetermined address.In this embodiment, in the initial setting mode or the like, themicroprocessor 211 previously sets the predetermined address of localmemory 212 in a register of the data transfer LSI 500. Setting of eachregister of data transfer LSI 500 will be described below.

(Arrangement of Registers)

FIG. 10 is a diagram showing the registers provided in the data transferLSI 500. The data transfer LSI 500 has LPBA registers 801, LSBAregisters 802, LSIBA registers 803, LNUM registers 804, SNUM registers805, LIP registers 806, STP registers 807, LOP registers 808, POPregisters 809 and an ABORT register 810.

The LPBA register 801 has a reference address fixed for to the addressesat which the microprocessor 211 writes data transfer information 600 inthe local memory 212 (this address is hereinafter called the list baseaddress). The microprocessor 211 writes the data transfer information600 in the local memory sequentially over an area beginning from thelist base address set in the LPBA register 801.

The LSB register 802 has a reference address set for the addresses atwhich the data transfer LSI 500 writes the end status information 700 inthe local memory 212 (this address will hereinafter be called the statusbase address). The data transfer LSI 500 writes the end statusinformation 700 sequentially in the local memory over an area beginningfrom the status base address.

The LSIBA register 803 has an address (hereinafter called the statuspointer address) fixed corresponding to the address on the local memory212 at which a pointer (hereinafter, called status pointer) is writtento indicate at what number address the data transfer LSI 500 has writtenthe end status information 700 when counting from the status baseaddress.

The LNUM register 804 has stored therein the number of pieces of datatransfer information 600 that can be assigned to one transferinformation list.

The SNUM register 805 has stored therein the number of pieces of the endstatus information 700 that the data transfer LSI 500 can write on thelocal memory 212.

The LIP register 806 has set therein by the microprocessor 211 theinformation (hereinafter, called the list write pointer) that indicateswhat number piece of information of transfer information list themicroprocessor 211 has written in the local memory 212 when countingfrom the list base address. The microprocessor 211 updates the LIPregister 806 each time it writes the data transfer information 600belonging to the transfer information list in the local memory 212.

The STP register 807 has the status pointer set therein. The datatransfer LSI 500 updates the STP register each time it writes the endstatus information 700 in the local memory 212. In addition, the datatransfer LSI 500 writes the value set in the STP register 807 at thestatus pointer address on the local memory 212.

The LOP register 808 has set therein by the data transfer LSI 500 apointer (hereinafter, called the list read pointer) that indicates whatnumber piece of information 600 of a transfer information list the datatransfer LSI 500 has read when counting from the list base address.

The POP register 809 has set therein the number of pieces of actuallyprocessed information 600 of a transfer information list belonging tothe data transfer information 600 that the data transfer LSI 500 hasread from the local memory 212. The microprocessor 212 compares the datatransfer process number written in the chain flag column 608 of the datatransfer information 600 with that actually processed by the datatransfer LSI 500 to check if the data transfer processing has beencorrectly carried out.

The ABORT register 810 is used to stop the data transfer processing thatthe data transfer LSI 500 is making. The ABORT register 810 has settherein a value (hereinafter, called SUS ABORT) indicating to stop whenthe data transfer LSI 500 has completed the data transfer processing foreach transfer information list. The SUS ABORT is a value of, forexample, “0x0004”. Also, it is possible that the ABORT register 810 hasset therein a value (hereinafter, called MP ABORT) indicating toimmediately terminate the data transfer processing that the datatransfer LSI 500 is performing. The MP ABORT is a value of, for example,“0x0001”. The operation that the data transfer LSI 500 makes forstopping the data transfer processing will be described later in detail.

The data transfer LSI 500 compares the list write pointer set in the LIPregister 806 with the list read pointer set in the LOP register 808,thereby making it possible to detect that an instruction to make newdata transfer process has been given by the microprocessor 211.

The data transfer LSI 500 can examine if there is any succeeding pieceof information of a transfer information list to be processed bycomparing the content of LIP register 806 with that of LOP register 808.

Thus, the microprocessor 211 can write each transfer information list inthe sequential addresses beginning from the list base address, while thedata transfer LSI 500 can read out each transfer information list fromthe sequential addresses beginning from the list base address. In otherwords, the queue for registering a transfer information list can becreated on the local memory 212.

The microprocessor 211 registers data transfer information in two queuesof the preferential queue for registering the data transfer informationfor the high-priority data transfer processing and the nonpreferentialqueue for registering the data transfer information for the usual datatransfer processing. Therefore, as shown in FIG. 10, the data transferLSI 500 has register pairs except the ABORT register 810, thus creatingtwo queues on the local memory 212.

Each of the above registers may be owned by the data transfer fetchcircuit 506 or DMA 501. In addition, the information stored in theseregisters may be stored in the local memory 212 or shared memory 220 inplace of the registers so that the data transfer LSI 500 can refer tothe local memory 212 or shared memory 220.

(Data Transfer Processing Using a Transfer Information List)

First, a description will be made of the case where only one queue inwhich a transfer information list is registered is used for the datatransfer processing that uses the transfer information list according tothis embodiment. FIG. 11 is a flowchart showing the flow of processes bywhich the data transfer processing is performed by using a transferinformation list.

The microprocessor 211 causes the local memory 212 to store apredetermined number of pieces of data transfer information 600 set inthe LNUM register 804 of data transfer LSI 500 as a transfer informationlist (S11001), and sets the list pointer in the LIP register 806 of datatransfer LSI 500 (S11002).

On the other hand, the data transfer LSI 500 waits for a new listpointer to be set in the LIP register 806 while it is comparing the LIPregister 806 and the LOP register 808 (S11003). When detecting that themicroprocessor 212 has set a list pointer in the LIP register 806(S11003: NO), the data transfer LSI 500 reads out the data transferinformation from the local memory 212 (S11004). Within the data transferLSI 500, the data transfer information fetch circuit 506 reads out thedata transfer information 600 from the local memory 212, and sets anecessary value for data transfer processing in the register of DMA 501(S11005). The data transfer LSI 500 makes processing for the datatransfer between the cache memory 230 and the buffer memory 214 on thebasis of the read data transfer information 600 (S11006). When finishingthe data transfer processing, the data transfer LSI 500 checks to see ifthe value set in the chain flag column 608 of that data transferinformation 600 is “1” (S11007). If it is “1” (S11007: YES), theprocessing goes back to step (S11004). However, the data transferinformation 600 read out this time in this step (S11004) is the datatransfer information 600 read out from the address that is located thedata length of data transfer information 600 ahead of the address fromwhich the data transfer LSI 500 previously read out the information 600.Thus, the data transfer LSI 500 sequentially reads out the data transferinformation 600 on the basis of the chain flag 608 of the read datatransfer information 600. The data transfer LSI 500 may read out all thepieces of data transfer information 600 belonging to the same transferinformation list at a time. In this case, the data transfer LSI 500decides that the data transfer information 600 having the same value setin the identification information column 607 belongs to the sametransfer information list.

If the value set in the chain flag column 608 of the data transferinformation 600 is not “1” (S11007: NO), the data transfer LSI 500writes the result of the data transfer processing in the local memory212 as the end status information 700 (S11008), and causes the statuspointer set in the STP register 807 to increment (S11009). The datatransfer LSI 500 writes the status pointer set in the STP register 807at the status pointer address on the local memory 212, and makes thelist pointer set in the LOP register 808 to increment, thus updating theLOP register 808 (S11010).

When the status pointer is updated by the data transfer LSI 500, themicroprocessor 211 detects the update (S11011: YES), reads out the endstatus information 700 from the local memory 212 and makes the endprocess according to the end status information 700 as, for example, ittransmits error information to the information processing apparatus 100or causes the display unit to display error (S11012).

Thus, when the microprocessor 211 writes a plurality of pieces of datatransfer information 600 as one transfer information list in the localmemory 212, the data transfer LSI 500 can sequentially read out each ofthe plurality of data transfer information from the memory. In addition,the data transfer LSI 500 can decide if the data transfer information600 read from the memory belongs to a data transfer information groupthat is processed in association by using the identification informationof data transfer information 600. Also, the data transfer LSI 500 canread out other data transfer information 600 belonging to the datatransfer information group mentioned above by using the identificationinformation column 607 or chain flag column 608 of data transferinformation 600 read from the local memory 212, and make the datatransfer processing for that information.

For example, in the disk array unit, the data to be written accompanyingthe data write request from other host apparatus is transferred to thecache memory. In this case, necessary successive addresses sometimescannot be secured for all the data to be written on the cache memory.Thus, according to the invention, when the data transfer processing fora plurality of pieces of information is desired to make continuously ona memory area of the data transfer source or transfer destination inwhich case the memory area is discontinuous, the first processor setsthe same processing identification information in multiple pieces ofdata transfer information that specify the discontinuous memory area,and causes the group of these pieces of data transfer information to beregistered in the queue. The second processor performs the data transferprocessing for the group of pieces of data transfer information with thesame processing identification information attached, therebycontinuously making the data transfer processing for the group ofinformation.

The data transfer LSI 500 may cause the local memory 212 to periodicallywrite the status pointer set in the STP register 807. In addition, thedata transfer LSI 500 may cause the local memory 212 to directly storethe status pointer without using the STP register.

The case of having two queues will be described.

In this embodiment, two queues of preferential queue and nonpreferentialqueue are created on the local memory 212. The microprocessor 211registers a transfer information list for high-priority data transferprocessing in the preferential queue, and another list for the normaldata transfer processing in the nonpreferential queue.

In this embodiment, the microprocessor 211 divides the task into twokinds of task: the task of I/O process according to the datainput/output request from the information processing apparatus 100, andthe task of internal processes such as local copy process, journalgeneration process, journal acquisition process, restore process orsnapshot process. The microprocessor 211 causes the local memory 212 tostore the number of registered pieces of data transfer informationassociated with each kind of task in the nonpreferential queue as atable (registered-number storing area). The microprocessor 211 acquiresthe number of registered pieces of the data transfer information for thedata transfer processing caused by the task of the kind different fromthe running task. If this number of registered information exceeds apredetermined number, the microprocessor 211 decides that the priorityof this data transfer processing is high. The microprocessor 211, whendeciding that the priority of the data transfer processing is high,causes the data transfer information 600 for the data transferprocessing to be registered in the preferential queue. When decidingthat the priority is not high, the microprocessor 211 registers the datatransfer information 600 in the nonpreferential queue.

In addition, the microprocessor 211 determines either one of the queuesin order for the data transfer information 600 to be registered inaccordance with the number of registered pieces of data transferinformation 600 that is associated with a task other than the runningtask and registered in the nonpreferential queue. Thus, themicroprocessor 211 can control the data transfer LSI 500 to make thedata transfer processing with good balance for each of a plurality oftasks to be executed.

The microprocessor 211 can also determine if the priority of datatransfer processing is high according to the priority level of therunning task. In this case, the microprocessor 211 controls the localmemory 212, for example, to store the identification information andpriority level of the task to be executed. The microprocessor 211 canalso control, for example, the priority of task to be stored as thepriority of data transfer processing. The microprocessor 211 determinesaccording to this priority if the data transfer information 600 isregistered either in the preferential queue or in the nonpreferentialqueue.

Moreover, the microprocessor 211 may set up a priority at each task tobe executed and determine one of the queues in which the data transferinformation 600 is to be registered in accordance with this priority.Thus, the microprocessor 211 can control the high-priority data transferprocessing to be made ahead of the low-priority data transferprocessing.

The flow of the transfer processing for data transfer information 600registered in the two queues as described above is the same as thatshown in FIG. 11. However, there is the following difference.

The data transfer LSI 500 first makes the comparison between the LIPregister 806 and the LOP register 808 for the preferential queue in thestep (S11003) to decide if any transfer information list is registeredin the preferential queue. If any transfer information list is notregistered in the preferential queue (the value set in the LIP register806 is equal to the value set in the LOP register 808), it makes thecomparison between the LIP register 806 and the LOP register 808 for thenonpreferential queue. The data transfer LSI 500, when any transferinformation list is registered in the preferential queue, does not makethe data transfer processing for the transfer information listregistered in the nonpreferential queue, but continuously makes the datatransfer processing for the transfer information list registered in thepreferential queue. Thus, the data transfer LSI 500 preferentially readsout the transfer information list from the preferential queue over thatregistered in the nonpreferential queue.

The microprocessor 21 can control the order of the data transferprocesses by, for example, registering the data transfer information 600for the high-priority data transfer processing at the head of thenonpreferential queue. However, if the data transfer LSI 500 read thedata transfer information 600 from the nonpreferential queue during thetime in which the microprocessor 211 was changing the order of pieces ofdata transfer information 600 registered in the nonpreferential queue,the data transfer processing could be performed in the order of datatransfer processes scheduled by the microprocessor 211. Therefore, themicroprocessor 211 would need to interrupt the operation of the datatransfer LSI 500 in order that it could rearrange the pieces of datatransfer information 600 to bring the high-priority information 600 tothe head of the nonpreferential queue.

According to the invention, the data transfer LSI 500 reads out the datatransfer information 600 from the preferential queue over thatregistered in the nonpreferential queue and makes the transferprocessing for that information 600. Therefore, the microprocessor 211can achieve the same effect as the registration of data transferinformation 600 at the head of the nonpreferential queue by registeringthe data transfer information 600 for the high-priority data transfer inthe preferential queue. Thus, the microprocessor 211 can preferentiallymake the data transfer processing for the data transfer information 600registered in the preferential queue without interrupting the operationof the data transfer LSI 500. In other words, the microprocessor 211 caneasily control to change the order of data transfer processes.

Also, the microprocessor 211 can preferentially make the data transferprocessing for the data transfer information 600 registered in thepreferential queue without changing the arrangement order of pieces ofdata transfer information 600 registered in the nonpreferential queue.Thus, when the data transfer information 600 is registered in accordancewith the priority, the necessary access to the memory can be suppressed,and hence the data transfer processing can be efficiently performed.

(Aborting Data Transfer Processing for Each Transfer Information List)

A description will be made of the processing for the data transfer LSI500 to abort the above data transfer processing.

As described above, the data transfer LSI 500 continuously makes datatransfer processing for a plurality of pieces of data transferinformation 600 set in the transfer information list during the time inwhich “1” is written in the chain flag column 608. In this case, whenthe microprocessor 211 writes SUSABORT in the ABORT register 810 of datatransfer LSI 500, the data transfer LSI 500, after finishing a sequenceof data transfer processes for a plurality of pieces of data transferinformation set in the above transfer information list, aborts the datatransfer processing for the succeeding transfer information list writtenin the local memory 212. When the microprocessor 211 writes MPABORT inthe ABORT register 810 of data transfer LSI 500, the data transfer LSI500 stops the above data transfer processing even when the processing isbeing executed. In other words, the microprocessor 211 writes theMPABORT in the ABORT register 810, thereby making it possible toforcibly stop the processing that the data transfer LSI 500 is carryingout. Thus, if the data transfer LSI 500 leaves the end statusinformation 700 not to be written in the local memory 212 for a constantperiod of time, the microprocessor 211 writes MPABORT in the ABORTregister 810, thereby controlling the data transfer LSI 500 to forciblystop its data transfer operation.

The flow of the process for the data transfer LSI 500 to stop the datatransfer processing is the same as that for the DMA controller 60according to the first embodiment to stop the data transfer processing.The data transfer LSI 500 makes the data transfer processing in place ofthe DMA controller 60. The above ABORT register 810 is used as theregister in which the abort command and forced termination command areset in place of the abort register 62.

The succeeding data transfer processing in the step (S4006) is made fora plurality of pieces of data transfer information 600 set in thetransfer information list. In addition, the nonpreferential transferinformation queue 21 and preferential transfer information queue 22 canbe created on the local memory 212 as the continuous memory areas thatbegin from the nonpreferential list base address and preferential listbase address, respectively. The end status queue 23 can be created onthe local memory 212 as the continuous memory area that begins from thenonpreferential status base address or preferential status base address.

In addition, the data transfer LSI 500 generates the above end statusinformation 700 as the result of having finished the data transferprocessing, and writes it in the local memory 212. At this time, thedata transfer LSI 500 reads out the identification information set inthe identification information column 607 of data transfer information600 from the local memory 212 and sets it in the identificationinformation column 701. The data transfer LSI 500, when the SUSABORT orMPABORT is set in the ABORT register 810, also sets “1” in thecorresponding bit of the end status code column 702.

Thus, according to the invention, the second processor (data transferLSI 500) makes the data transfer processing for a group of data transferinformation (data transfer information group of which the informationpieces are coupled by the chain flag column 608) with the sameprocessing identification information attached. After the transferprocessing for all the group of data transfer information is finished,if the abort command is set in the register, the succeeding datatransfer processing is stopped. Therefore, the second processor can stopthe data transfer processing at the time when the sequence of datatransfer processes based on the data transfer information group has beencompleted. Thus, the second processor never stops the data transferprocessing during the time in which the processing for the plurality ofsuccessive data transfer processes is being executed. Therefore, thereduction of the data transfer ability of the whole data transferapparatus due to the stop of operation can be suppressed to the minimumsince the second processor never stops the data transfer processing.

Moreover, when the abort command is set in the ABORT register 810, thedata transfer LSI 500 sets in the end status code column 702 of endstatus information 700 the abort flag that indicates if the datatransfer processing has been stopped. Therefore, the microprocessor 211is able to know that the data transfer LSI 500 has stopped the datatransfer processing in accordance with the abort command set in theABORT register 810 of data transfer LSI 500 by referring to the endstatus code column 702 of end status information 700 stored in the localmemory 212. Accordingly, the microprocessor 211 can see indirectlythrough the local memory 212 that the data transfer LSI 500 has stoppedthe data transfer processing without monitoring the operation of thedata transfer LSI 500 and without directly receiving the notice ofhaving stopped the data transfer processing from the data transfer LSI500. Thus, the microprocessor 211 can efficiently operate.

Other Embodiments

While the microprocessor 211 writes each transfer information list inthe local memory 212 in the above embodiment, each piece of datatransfer information can be written. For example, information of whatnumber piece of the multiple pieces of data transfer information 600 isstored in the local memory 212 is set in the LIP register 804 or PRLIPregister 814 of the data transfer LSI 500 so that, when themicroprocessor 211 writes the multiple pieces of data transferinformation 600, the information of the number can indicate that thelast one of the multiple pieces of data transfer information 600 hasbeen written. Then, the data transfer LSI 500 adds the data length ofdata transfer information 600 to the nonpreferential list base addressor preferential list base address repetitively the number of timescorresponding to the number of pieces of information set in the LOPregister 808 or PRLOP register 818, and thereby finds the addresses atwhich the data transfer information 600 is read from the local memory212 so that the information 600 can be read from the memory. The datatransfer LSI 500, when the chain flag column 608 of the read datatransfer information 600 is “1”, also adds the data length of datatransfer information 600 to the read address again and again to continuethe reading of data transfer information 600. Therefore, the informationabout data transfer is transmitted not in a unit of a transferinformation lists but in a unit of a piece of transfer information 600from the microprocessor 211 to the data transfer LSI 500, so that thevariable-length data transfer information 600 can be transmitted andreceived.

Also, while the data transfer information 600 is written in the localmemory 212 that the microprocessor 211 manages in the above embodiment,a memory device such as the shared memory 220, cache memory 230 or othermemory to which the microprocessor and data transfer LSI can similarlyaccess may be used in place of the local memory 212.

In addition, the present invention can be applied to the disk controlunit 240. If the disk control unit 240 has a microprocessor, a localmemory, an interface for access to the storage device 300, and a datatransfer LSI, the data transfer processing for the data to betransferred between the cache memory 230 and the storage device 300 canbe made in the same way as in the channel control unit 210.

Furthermore, the invention can be applied to the storage device controlapparatus having the communications interfaces 213 (communicationsinterface unit), microprocessors 211, local memories 212, data transferLSI 500, and interfaces (storage device interfaces) to the storagedevice 300 integrally arranged within the channel control unit 210. Inthis case, the data transfer LSI 500 can make the data transferprocessing between the storage device 300 and the buffer memory 214 inplace of the cache memory 230.

The above embodiments have been described in order to easily understandthe invention, and thus the present invention is not limited to thoseembodiments. The present invention can be changed and modified withoutdeparting from the scope of the invention. In addition, the inventionalso includes the equivalents of the changes and modifications.

1. A storage device control apparatus comprising: a communicationsinterface unit having a buffer memory for receiving a data input/outputrequest transmitted from an information processing apparatus to astorage device and storing said received data input/output request; astorage device interface unit for transmitting and receiving datato/from said storage device; a random access memory (RAM) having apreferential transfer information queue and a non-preferential transferinformation queue for registering data transfer information thatincludes information for specifying a memory area of said buffer memoryand information for specifying a memory area of said storage device,said preferential transfer information queue having a higher transferpriority than said non-preferential transfer information queue; acentral processing unit (CPU) for causing said data transfer informationto be registered in said preferential transfer information queue or saidnon-preferential transfer information queue; and a direct memory access(DMA) controller that performs data transfer processing to transfer databetween said buffer memory and said storage device, said DMA controllerhaving start and abort registers, wherein said DMA controller reads outsaid data transfer information registered in said preferential transferinformation queue, performs said data transfer processing on a basis ofsaid read data transfer information, and decides if subsequent datatransfer information that follows said read data transfer information isregistered in said preferential transfer information queue, if saidsubsequent data transfer information is registered in said preferentialtransfer information queue, said DMA controller reads out saidsubsequent data transfer information from said preferential transferinformation queue, and performs said data transfer processing on a basisof said read data transfer information, and if said subsequent datatransfer information is not registered in said preferential transferinformation queue, said DMA controller reads out said data transferinformation from said non-preferential transfer information queue, andperforms said data transfer processing on a basis of said read datatransfer information from said non-preferential transfer informationqueue.
 2. A storage device control apparatus according to claim 1,wherein said RAM further comprises an end status queue for registeringan end status of a data transfer processing by said DMA controller inresponse to completion of the data transfer processing, and said CPUchecks the end status to inform abnormality of data transfer processing.3. A storage device control apparatus according to claim 1, wherein inresponse to detection of the subsequent data transfer information fromsaid preferential transfer information queue or said non-preferentialtransfer information queue, said DMA controller continues a datatransfer processing corresponding to the subsequent data transferinformation independently of writing into the start register.
 4. Amethod for accessing a storage unit comprising: a first processorwriting a plurality of data transfer information to either a first queueor a second queue, each data transfer information indicating a transferoperation, a location in a buffer memory, and a location in said storageunit; a second processor retrieving data transfer information fromeither the first queue or the second queue; and the second processortransferring data between the location in the buffer memory and thelocation in the storage unit of the data transfer information retrieved,based on the transfer operation of the data transfer informationretrieved, wherein the second processor preferentially retrieves datatransfer information that is stored in the second queue over datatransfer information that is stored in the second queue, whereby if datatransfer information is stored in the first queue and data transferinformation is stored in the second queue, then the second processorretrieves data transfer information stored in the second queue, wherebyif data transfer information is stored in the first queue and there isno data transfer information stored in the second queue, then the secondprocessor retrieves data transfer information stored in the first queue.5. A method for accessing a storage unit according to claim 4 furthercomprising: determining, during the step of the second processortransferring data, whether an abort indication has been signaled; and ifan abort indication has been signaled, then ceasing the step of thetransferring data between the location in the buffer memory and thelocation in the storage unit of the data transfer information retrieved.6. A method for accessing a storage unit according to claim 4 furthercomprising: detecting an abort signal; ceasing the step of thetransferring data between the location in the buffer memory and thelocation in the storage unit of the data transfer information retrievedwhen the abort signal is a first type of abort indication; completingthe step of the transferring data between the location in the buffermemory and the location in the storage unit of the data transferinformation retrieved when the abort signal is a second type of abortindication; and setting a status indicator to indicate either the firsttype of abort indication or the second type of abort indication based onthe abort signal.